The spectator is encouraged to inspect the glass to make sure that it is solid. It can be bashed with a solid piece of wood showing or banged on a hard wooden surface to show it to be solid and strong. You take the glass back and concentrate on it and with an explosion reminiscent of a rifle shot and exactly on your command the bottle shatters completely. There are also hundreds of other variations on the handling, for example you can just apparently blow into the glass and it shatters.
Bologna Bottles, sometimes known as The Devil's Coke Bottles, have been around for decades and are often seen in science experiments. These glasses are made in exactly the same way and are real drinking glasses. They are made by heating the glass to extreme temperatures and then rapidly cooling the inside, whilst slowly cooling the outside. This puts incredible tension on the glass on the inside of it and even though you can hit it hard on a wooden surface, it won't break. To break it, you drop something small and brittle in it, something like a small piece of broken glass, or ceramic or you get a small piece of metal with it that you can also use. You can either hold the brittle object in your hand and as you hold the top of the glass, just secretly drop it inside and wait or you can have something inside already (drop it in carefully) and just shake it and wait and it will just shatter on it's own..
Dimensions: Height - 18cm, base width - 6cm, 200ml.
Glass measurements: height - 18.5cm, base width - 5cm